1. Technical Field
The present invention relates to a position detection apparatus capable of detecting the position pointed with a pointing element on an operation surface.
2. Related Art
JP-A-2012-150636 discloses an interactive projector having the function as a position detection apparatus. The interactive projector can project a projected screen on a screen, capture an image containing a pointing element, such as a light emitting pen and a finger, with a camera, and detect the position pointed with the pointing element by using the captured image. That is, when the front end of an object is in contact with the screen, the interactive projector recognizes that a predetermined instruction, such as a drawing instruction, is inputted to the projected screen and draws the projected screen again in accordance with the instruction. A user can therefore input a variety of instructions by using the projected screen as a user interface.
To detect the position pointed with the pointing element, the interactive projector irradiates the pointing element with detection light, such as infrared light, and captures an image of the detection light reflected off the pointing element with the camera. To detect the position pointed with the pointing element on the basis of the captured image, contrast between the pointing element and the projected screen is used to determine the position of the pointing element in the image. To this end, the image captured with the camera desirably provides sufficient contrast between the pointing element and the projected screen.
The inventor of the present application, however, has found that it is not always easy to sufficiently increase the contrast between the pointing element and the projected screen, and that sufficient contrast cannot be provided depending on the detection light irradiation state. The problem is not limited to an interactive projector but is a common problem in a position detection apparatus that detects a pointed position pointed with a pointing element on an operation surface.